Pure populations of primary lymphocytes, monocytes, and dendritic cells will be separated from normal human blood via physical cell separation and FACS. Monoclonal antibody (MAb) markers defining various differentiated cell phenotypes will be used to identify and purify specific subpopulations of these cell types. The cells will be infected with HIV-1 and virus growth and gene expression will be evaluated by FACS, PCR, and other assays. Cell subpopulations which support HIV replication in vitro can then be assessed from HIV-seropositive blood to determine which subpopulations are viral reservoirs in vivo.